The objectives of this project are to obtain quantitative information about the total population of lysosomal dense bodies contained within cells of the enamel organ, and to determine if there are significant alterations in the relative size of this population, or the activity of enzymes present therein, over the course of amelogenesis. In one part of the project, conventional EM stereological techniques are used to establish the volumetric distribution of lysosomal dense bodies within each cell layer of the enamel organ at progressive stages during development of enamel, that is, (1) before cell differentiation (proliferative stage), (2) at the beginning and at the end of the appositional growth of the enamel layer (secretory stage), and (3) during the period when there is an abrupt decline in the amount of extracellular organic material within the maturing enamel layer (maturation stage). In a second part of the project, conventional biochemical techniques are used to quantitate and compare the gross activity of several "lysosome-associated" enzymes between the stages of enamel secretion and enamel maturation (e.g., acid phosphatase, inorganic trimetaphosphatase, lipase, DNAse, glycosidase, proteinase). In a third part of the project, conventional EM cytochemical techniques are used to obtain a qualitative assessment of the ultrastructural distribution of these same enzymes within cells of the enamel organ. The continuously erupting rat incisor is used as the experimental system for these studies.